Field
Exemplary embodiments relate to an LED driving circuit for continuously driving an LED, an LED lighting device including the same, and a driving method. More particularly, exemplary embodiments relate to an LED driving circuit for continuously driving an LED capable of compensating for an optical output of LED lighting using an energy chargeable/dischargeable element and/or circuit, an LED lighting device including the same, and a driving method.
Discussion of the Background
LED driving is generally based on a DC driving type. The DC driving type has to include an AC-DC converter such as an SMPS. The power converter causes problems of increasing manufacturing costs of lighting fittings, making it difficult to miniaturizing the lighting fittings, reducing energy efficiency of the lighting fittings, and shortening a life of the lighting fittings due to a short life of the power converter.
To solve the problems of the foregoing DC driving type, an AC driving type for an LED has been proposed. However, in the case of a circuit based on the technology, a power factor may be reduced due to a mismatch between an input voltage and a current output from the LED and a flicker phenomenon that a user recognizes flickering of lighting due to a long non-emission section of the LED may occur.
To solve the problems of the foregoing AC driving type for an LED, a sequential driving type for an AC LED has been proposed. According to the sequential driving type for an AC LED, under the situation that the input voltage is increased over time, a first LED first starts to emit light at Vf1, a second LED is connected to the first LED in series to start to emit light at Vf2 which is a voltage higher than the Vf1, and a third LED is connected to the second LED and the first LED in series to start to emit light at Vf3 which is a voltage higher than the Vf2. In addition, under the situation that the input voltage is decreased over time, the third LED first stops emitting the light at the Vf3, the second LED stops emitting light at the Vf2, and the first LED finally stops emitting light at the Vf1, such that an LED driving current is designed to be approximate to the input voltage. According to the AC LED sequential driving type, the LED driving current is converged like an AC input voltage, and as a result a power factor may be improved. However, the flicker phenomenon still occurs in the non-emission section in which the input voltage does not reach the Vf1 and a light emitting time for each LED light emitting module is different to make optical characteristics of the lighting fittings non-uniform.
Meanwhile, to solve the problem of the AC LED sequential driving type as described above, various technologies to remove a non-emission section using a smoothing capacitor, a power factor correction circuit, etc., have been proposed. However, according to the foregoing technologies, a total harmonic distortion (THD) may be rather worse due to device characteristics in which a current is suddenly increased at timing when the smoothing capacitor starts to perform the charging. Further, since the smoothing capacitor needs to maintain a voltage which is equal to or more than at least Vf3 in order to drive all the LEDs in the non-emission section, the smoothing capacitor requires high capacitance. As a result, the smoothing capacitor is expensive and it is difficult to miniaturize the LED lighting fitting.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the inventive concept, and, therefore, it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.